A photodetector is equipped with a plurality of photodiodes, which are aligned one-dimensionally or two-dimensionally, and integrating circuits, which include amplifiers and capacitors, and may be equipped in some cases with a signal processing circuit at a more downstream position. With this photodetector, charges of amounts, which are in accordance with the intensities of incident light on the respective photodiodes, are output from the photodiodes, these charges are accumulated in the capacitors, and voltages, which are in accordance with the amounts of these accumulated charges, are output from the integrating circuits. Based on the voltages output from the integrating circuits in accordance with the amounts of charges generated respectively at the plurality of photodiodes, the light, made incident on a light receiving part wherein the plurality of photodiodes are aligned, is detected.
As such a photodetector, the arrangement disclosed in Japanese Published Unexamined Patent Application No. Hei 11-287863 is known. With the photodetector disclosed in this publication, a first substrate, wherein a plurality of photodiodes are aligned two-dimensionally, and a second substrate, wherein integrating circuits, etc., are disposed, are connected to each other by a flexible cable. Also, a switch array is disposed on the first substrate on which the plurality of photodiode arrays are aligned, and by the on/off of the respective switches in this switch array, one or more of the photodiodes of the two-dimensionally aligned plurality of photodiodes are selected and connected to the integrating circuits.